Apoptosis is a genetically programmed process of cell death that has recently been implicated in a number of important diseases including a variety of reproductive disorders. In mammals, greater than 99.9% of all oocytes are lost in a process termed atresia which is characterized by massive apoptosis of the supporting granulosa cells. Morphologically, one of the earliest conserved events of dying cells is cell shrinkage and recent studies by the principle investigator and others have identified and rapid and specific efflux of intracellular K+ thought to drive this change. In these studies, K+ efflux caused cell shrinkage by osmotically drawing water out of the dying cell and it was assumed that this water would leave by simple diffusion through the lipid bilayer. In this proposal we challenge that assumption and hypothesize that water movement during apoptosis is mediated by preliminary data that general inhibitors of aquaporins block granulosa cell shrinkage during apoptosis. In addition, these inhibitors also block DNA degradation, leading us to further hypothesize that aquaporin-mediated water loss is critical to down-stream apoptotic events. PCR studies demonstrate that aquaporin-8 and -9 mRNA are expressed in granulosa cells and preliminary antisense studies point to a major role for aquaporin-9 in both cell shrinkage and DNA degradation during cell death. We thus propose a series of studies to assess the role of aquaporins in mediating wa6ter movement and their importance to the overall apoptotic process. These studies will provide the critical pool-of-concept data necessary to submit an R01 application. Defects in aquaporins have been casually implicated in a number of important ailments such as congestive heart failure, pulmonary obstruction cystic fibrosis cataracts asthma and stroke. Thus, it seems likely that alterations in their function may underlie some of the serious diseases associated with apoptosis such a cancer and AIDS as well as those which adversely effect women's health such as premature ovarian failure, ovarian cyst formation and ovarian cancer.